Can I get secondary service connection for a condition aggravated by a service-connected disability if there's no baseline documentation before I was diagnosed?

Secondary service connection, including aggravation, is governed by 38 CFR 3.310. There are two paths: direct secondary connection, where a service-connected condition caused a new condition, and aggravation, where a nonservice-connected condition existed and was made chronically worse by a service-connected disability. For an aggravation claim, VA is supposed to determine the baseline severity of the nonservice-connected condition before the aggravation occurred, then compare it to the current, more severe level. The difference between those two levels is what gets compensated, and that comparison is typically done through medical evidence and opinion, not by the veteran personally documenting a baseline.

Not having a pre-diagnosis baseline does not automatically defeat an aggravation claim, but it does make it harder to prove, because the rating decision will often come down to what a medical opinion says about the likely course and severity of the condition absent the aggravating factor. A strong nexus letter or compensation and pension examiner opinion can still address baseline severity retroactively using medical judgment, prior treatment records, risk factors, and objective findings like ejection fraction trends, even without a documented pre-diagnosis baseline. If the evidence is too sparse for an examiner to render a baseline opinion with any confidence, VA may deny the aggravation theory or could, in some cases, grant it as a direct secondary connection instead if the hypertension is shown to have caused the heart failure outright rather than simply aggravated it.

On the rating question, heart conditions are rated under 38 CFR 4.104, and an ejection fraction of 30 percent generally corresponds to a 60 percent rating under those criteria if service connection is established, whether by direct or secondary theory. If VA grants the claim as aggravation but cannot identify any measurable baseline severity to subtract, in practice the condition is often rated at its full current severity rather than reduced to zero, but outcomes depend heavily on the specific medical evidence and how the rating decision characterizes the aggravation.

Because this hinges entirely on obtaining a well-supported medical nexus opinion addressing both causation/aggravation and baseline severity, the concrete next step is to get a cardiologist or an independent medical examiner to review all available records and provide a written opinion specifically addressing whether the hypertension aggravated the heart failure and, if possible, what the condition's probable baseline severity would have been absent that aggravation, then submit that opinion with the claim or appeal.